Ultrasound question

I just found out I am pregnant and called My doctor to schedule my first appointment. The nurse told me that they don't do any ultrasounds until 20 weeks which I find strange. Everyone that I know that has been pregnant has had a transvaginal ultrasound at around 8 weeks. This makes me kind of nervous especially seeing as this is my 3rd pregnancy and the first 2 miscarried. Does anyone know anything about this?